This project assesses the various techniques proposed for early stopping of clinical trials in the face of unexpected evidence of the failure or success of a particular regimen, prior to the scheduled termination of a trial. Distribution theory for these procedures in either mathematically intractable or only known asymptotically. A computer simulation study for comparison of the various procedures is being considered. OBFS organized an invited paper session at the Spring 1981 Biometrics meeting concerning this topic. It is expected that the papers from this session will be published together.